The Correspondence of Thomas Jefferson

By Subject


I will begin with the subject of your bridge, in which I feel myself interested; and it is with great pleasure that I learn, by your favor of the 16th, that the execution of the arch of experiment exceeds your expectations. In your former letter, you mention, that instead of arranging your tubes and bolts as ordinates to the cord of the arch, you had reverted to your first idea, of arranging them in the direction of the radii. I am sure it will gain, both in beauty and strength. It is true that the divergence of those radii recurs as a difficulty, in getting the rails on upon the bolts; but I thought this fully removed by the answer you first gave me, when I suggested that difficulty, to wit, that you should place the rails first, and drive the bolts through them, and not, as I had imagined, place the bolts first, and put the rails on them. I must doubt whether what you now suggest, will be as good as your first idea; to wit, to have every rail split into two pieces longitudinally, so that there shall be but the halves of the holes in each, and then to clamp the two halves together. The solidity of this method cannot be equal to that of the solid rail, and it increases the suspicions part of the whole machine, which, in a first experiment, ought to be rendered as few as possible. But of all this, the practical iron men are much better judges than we theorists.

to Thomas Paine, 23 December 1788